Onii-chan!
by sarahsanchez
Summary: What happens when Rin is Yukio's younger brother?


"-channn~ Nii-chan! Get upppp!"

The older of the twin brothers grumbled as he was awoken by a noisy Rin straddling his previously sleeping form.

"Rin, how many times do I have to tell you to normally wake me up in the morning?" Yukio grumbled while shoving his little brother on the ground and making his way out of bed. He swiftly made his way to the bathroom with flushed cheeks and a boner as his twin whined and got off of the ground while rubbing his head pouting.

"Nii-chan is too mean." Rin pouted and crossed his arms while looking away from his older brother.

Yukio payed no mind to this accusation and slammed the door shut. He splashed some cold water on his flushed face to cool himself down. He was ashamed to admit that he had been dreaming less than appropriate things about his adorable little brother. As mature and put together as he seemed, his teenage hormones controlled his dreams in the realm of sleep.

He looked at himself in the mirror. He looked like a zombie due to his lack of sleep. His eyes had bags under them and his face was pale and colorless. His eyes trailed down his body to look at his erection that was throbbing through his pajama pants. He cringed and sighed while walking over to the shower. He turned the water onto the coldest setting and stripped. Shivers went up his spine and he groaned. He needed to get rid of this damn thing as soon as possible. He stepped into the shower and cringed as he felt the freezing water run all over his toned body. Goosebumps covered his skin and he stood there for a while. He breathed deeply in and out to calm himself down.

 _What the hell is wrong with me?_

 _. Time skip ._

Yukio slammed the door of their dorm room and open and stomped up the stairs. To say he was pissed would be an understatement. His blood was boiling with rage and his hands were fisted at his side.

He had been on a mission through the school hours and well into the night. He had expected his little brother to be good while he was away, but Mephisto had informed him of some bad news. Apparently, Rin flared up in front of his entire class. He clearly didn't think about or understand how annoying the whole situation was.

It was a couple of hours past midnight. Yukio was so tired and so mad at his little brother. He cared about him and didn't want him to get in trouble or worse.

He sprinted down the hall and to the room that they shared. Rin was laying on his bed still awake.

"O-oh! Nii-chan! I was waiting for you because I couldn't sleep without you and I just missed you so muchhhh~!" Rin said innocently while pretending not to see the angry expression that was spread across his brother's face. In one sudden movement, Rin was pinned to the bed by his older brother. Yukio figured that he might as well take advantage of his brother and make all of his fantasies come true.

He whimpered in fear and squirmed beneath him.

"O-onii-chan! I didn't mean too! It was an acciden-ah!" His sentence was cut off as Yukio ripped off the oversized shirt that his twin was wearing. He licked his lips at the sight of his brother's scrawny feminine form. His hands wandered down the small teenager's body and pulled down his pants and underwear in one movement. He growled at the sight that was before him. Rin lay there with his arms being held above his head with one of Yukio's large hands. His cheeks were flushed and his chest was moving up and down in due to his heavy pants. His blue eyes were drooped and glazed over and his tongue stuck out slightly causing a trail of saliva to run down his chin.

"N-nii-chan...what are you doing?" He stuttered and looked away awkwardly while his twin violated him.

"I suppose you know what the problem is, hmm? I think you guessed that I would be pretty pissed about this whole situation right?"

"Onii-chan...I'm so sorry! I'll do whatever you want, just forgive me!" Rin said while breaking down and crying.

"You're willing to do _anything_ , Rin?" Yukio said while smirking evilly.

"Y-yes..."

"Rin... I'm going to fuck you." Yukio whispered in his twin's ear while licking the point at the end.

Rin gasped at this statement and looked at Yukio with wide eyes. He then drooped his head down in defeat. He couldn't win against his Nii-chan.

"Nii-chan... *hic* p-please...fuck me..." Rin said while tears still trailed down his porcelain cheeks.

Yukio pounced as he heard these words. He roughly pressed his lips against his Rin's soft pink lips. He grabbed his chin and forced his mouth open while taking the opportunity to shove his tongue into the smaller boy's mouth. Rin moaned into Yukio's needy mouth and wrapped his long thin arms around the other boy's neck.

Rin broke away from the kiss causing a trail of saliva to connect each of their mouths together.

"O-onii-chan...it's hot. It's really hot..." Rin said while panting and looking needily into Yukio's eyes with his eyebrows furrowed. Yukio chuckled at his brother's adorable reaction to this situation. He obviously didn't know much about the whole... _process_.

"Yes, it's hot," Yukio mumbled a reply as he sat both of them up. Rin's eyes widened as he stared down at his brother's huge member.

"W-what happened?!" Rin said as he bent down to get a closer look.

"You really don't know, Rin?" He shook his head. His face looked to be completely confused about what was happening. This made Yukio want him even more. He wanted to violate his little brother. He wanted to taint him and make him his. He wanted to fuck him so hard that he would _never_ think of making him angry ever again.

"Rin, open your mouth."

Rin cocked his head to the side in confusion. He was too innocent for his own good. He didn't know what he was doing, but he knew he had to obey his Nii-chan.

"Now. Suck." Yukio said as he shoved his dick into his little brother's hot mouth.

Rin whined and begged against the huge cock that was hitting against the back of his throat. The vibrations made Yukio clench his jaw to hold back a moan. He thrust hard until his entire member into Rin's mouth.

A jolt of pleasure ran throughout Rin's entire body causing him to suck hard on the dick in his mouth. It was weird, but Rin was getting pleasure without even touching himself. He felt a surge of adrenaline and bobbed his head up and down. He slid Yukio out of his mouth and grabbed the shaft into his hands. He noticed the liquid that seeped out of the tip and looked at it with curiosity. Rin looked up with wide blue eyes at his panting older brother.

"Ne, Nii-chan...what _is_ this?" Rin said innocently while rubbing the tip and getting the liquid all over his fingers. Yukio groaned and threw his head back.

"N-ne...Nii-chan? C-can I taste it...?"

Yukio's response was thrusting his member into Rin's mouth again. Rin looked at him with furrowed eyebrows and wide eyes. Yukio grabbed the blue locks and roughly thrust into the tiny boy's mouth until he felt his release coming.

"Rin, open wide."

Rin took the dick out of his mouth and obeyed his Nii-chan. His tongue stuck out and he closed his eyes tightly in anticipation. He looked so submissive that Yukio couldn't hold back anymore. He came hard inside of Rin's mouth. Cum dripped down all over the young boy's face and completely filled his open mouth.

Rin didn't know what it was, but he liked the taste. He swallowed the thick liquid that filled his entire mouth and dripped down the sides of his chin.

"Onii-chan... yummy...!" Rin said as he licked the rest of cum off of his brother's member greedily.

Yukio couldn't hold back anymore. He grabbed Rin's wrists and shoved him down on the bed causing him to yelp at the suddenness.

Yukio quickly shoved three fingers into Rin's mouth, coating his fingers in the makeshift lube. He felt the younger boy's body tense up in anticipation as he felt three fingers prodding at his pink hole. He whimpered and hid his face in his hands. Yukio used his free hand to grab his twin's hands and pinned them down against his stomach.

Without hesitation, Yukio shoved three curled fingers into the tight hole.

"Ahh..! Hah...O-onii-chaaa~nn, w-what are you doing...? I-it hurts really bad!"

Yukio showed no mercy as his fingers thrust quickly and harshly in and out of Rin. The demon was nothing more than a moaning mess that could only defensively squirm underneath his dominant brother.

"Ahnnn~ O-onii-chan...I-I...just put it in...~!" Rin cried out as he felt something building up in his lower regions that had to be released. Yukio took his exorcist jacket and tie off at an agonizingly slow pace. Rin looked at his older brother with a pained expression.

"Nii-chan...please..."

Yukio threw his jacket on the floor and used the tie to bind his brother's wrists to the headboard. He climbed on top of the trembling demon and put his mouth next to his pointed ear.

"Put what in?"

"I-I don't wanna say it," Rin said awkwardly while a fierce blush spread across his cheeks.

"If you don't say it, I'm going to leave without letting you cum," He whispered teasingly into the bluenette's ear. Rin mewled out and bit his lip so hard that a trail of blood ran down his chin.

"Nii-chan, I-I want your...uh..."

"Say it," Yukio growled lowly as he grabbed the other boy's smaller member into his large hands.

"Agh! Nii-chan, I want your dick in me! J-just l-let me cum! Please!" Rin begged with a desperate look on his face.

Yukio couldn't hold back anymore.

He shoved his member inch by inch into his little brother's tiny hole. Rin struggled against his restraints and shut his eyes as tight as possible.

" _Nii-chan!_ Stop, i-it's not gonna fit! _W-wait!"_ Rin screamed and moaned beneath him defenselessly due to the fact that his hands were tied above his head.

" _KYA!_ Y-YUKIO~" Rin screamed out as Yukio ignored his pleas and rammed his entire cock into his heat. Rin's back arched to get more contact with Yukio's bare chest.

He felt so _full_.

All he could do was writhe beneath Yukio who was unrelentlessly slamming into him.

"Hah! Ahnn~ Onii-channn! M-more! Go harder!" Rin cried out, desperate to feel the pleasure being given to him. Yukio grabbed his feminine hips and slammed into him at inhuman speeds.

"Ngh...Yukioo~" Rin moaned out.

"What did you just call me?"

"Uh...onii-chan?"

Yukio ripped the tie that was holding Rin's hands against the bed and pulled out. Rin whined at the feeling of emptiness. He was harshly grabbed and turned so that his face was shoved into the pillow and his ass was stuck in the air. Yukio almost drooled at the sight. He wasted no time and plunged himself as deep as he could in one harsh thrust.

"Ha~ah~Ah~ Nii-chan! Don't stop!" Rin cried out while pushing his hips back to meet each damaging thrust. He turned his head around and noticed that Yukio's shirt was still on. He was about to pout but couldn't help but think about how much of a whore he felt like. It was exciting- the feeling of being used by Yukio. He would do anything for his older brother no matter what.

The adorable sounds coming out of Rin's mouth were only turning Yukio on even more. The way he mewled and whipped his tail around made him seem like an oversized cat. He was so innocent and the fact that he was before Yukio now with a dick up his ass caused him to thrust even faster.

Rin's small frame trembled and twitched under him and he felt the demon's walls clench around him.

"Ha~ah~Y-Yuki! Nii-chan! I-I... AH!" Rin screamed out in pleasure as came. His tiny body slumped down while his ass was being held up and fucked by Yukio. He moaned weakly as he felt his brother pound mercilessly into him due to the fact that he was close.

" _Nii-chan_ ," Rin whimpered out as he felt his brother's seed fill him up and coat his entire lower half.

His eyes drooped in relaxation and he snuggled into the bed. He was just about to fall asleep when he felt Yukio's member plunge into him again. He tried to get up and away from his horny brother, but it was no use. He was shoved down onto the mattress again and fell apart under Yukio's touch.

"Nii-chan...I can't take anymore..." Rin begged while panting and looking desperately at his brother to just let him sleep in peace.

"Remeber Rin, this is your punishment," Yukio said while stroking the base of his long whip-like tail with fur at the end. He shuddered at the touch and melted back into the sheets.

"B-but... _Onii-chan_!"


End file.
